Various derrick operations require repetitive handling of heavy tubulars, for example lengths of drill pipe, drill collars, subs, and logging tools. Such tubulars must be carefully positioned over the mouse hole or hole centre in order to make up and convey strings of tubulars downhole. Repetitive manipulation of heavy tubulars in close proximity to various rig personnel poses a site safety hazard, and various operating protocols are typically implemented to minimize the risk of hazardous incidents.
Generally, tubulars are lifted and lowered to the work area by a pipe handling system associated with a catwalk assembly. In the case of drill pipe, a rack of pipe lengths is typically placed on either side of the catwalk, and the pipe handler receives individual lengths of pipe from each rack for advancement towards the derrick floor along a trough. Existing methods for raising the trough towards the work area generally involve extending a support leg beneath one or both ends of the trough, the support leg(s) pivotally attached to both the catwalk assembly and the trough to lift and advance the trough towards the derrick floor. A skate advances the drill pipe along the trough so it may be received by rig personnel and/or vertical handling equipment, for attachment to previous lengths of drill pipe already downhole.
Similarly, break-down of long tubing strings requires careful removal and reorientation of tubular sections from the derrick onto transportable pipe racks, with minimal handling by rig personnel.
Prior catwalk-based handlers typically lift lengths of pipe from below and/or have sliding components that travel along the base frame during lifting or lowering. With so many moving and advancing components, there is increased hazard to personnel using the catwalk, and increased likelihood of dropping the tubular.
U.S. Pat. No. 6,994,505 to Hawkins, describes a lift frame pivotally attached to a base, for use in lifting lengths of pipe to a rig floor. The front end of the lift frame is raised by a lift arm to at least rig height. A telescopic trough advances from the lift frame to deliver the pipe to the rig floor.
CA 2,224,638 describes a pipe handler in which a pivoting leg member raises the front end of a pipe trough towards a rig floor, and the trough also advances longitudinally along the base frame.
U.S. Pat. No. 4,235,566 to Beeman and Beeman describes a pipe-conveying catwalk assembly in which a pipe is carried on a trough extension that is nested in a boom arm. The extendable boom arm is driven up a ramp along a track towards the rig by a pair of swing arms pivotally attached to the frame.